1. Field of the Invention
This present invention relates to hyperbranched amine-functional polyesters, i.e., polyaspartate esters, and to a method for their preparation by the self condensation of hydroxy aspartate esters via a transesterification reaction.
2. Description of the Prior Art
Coating compositions containing, as binders, polyisocyanates in combination with polyaspartates containing secondary amino groups are known and disclosed in U.S. Pat. No. 5,126,170 and also DE-OS 2,158,945. However, the functionality of these polyaspartates is limited to the functionality of the starting polyamine. Higher functionalities are required to provide increased hardness as well as solvent resistance. However, as the functionality of these polyaspartates increases, the viscosity also increases such that more solvent is required to reduce the viscosity of the composition to typical application levels.
It is an object of the present invention to provide highly functional resins, which have a low viscosity and may be used for various applications, especially for the production of coatings having a high degree of hardness and solvent resistance.
This object may be achieved with the hyperbranched amine-functional polyesters according to the present invention that are described in more detail below. It is surprising that these amine-functional polyesters can be prepared since it would be expected that they would not be stable enough to satisfy this object due to the well known fact that amines cause the degradation of ester groups.
Hyperbranched polymers have been disclosed in the prior art. See, for example, PCT application WO 93/21259, "The Solid-Phase Synthesis of Dendritic Polyamides" by Uhrich et al, Polymer Bulletin 25, pg. 551 to 558 (1991); "Synthesis, characterization, And Curing of Hyperbranched Allyl Ether-Maleate Functional Ester Resins" by Johansson et al, J. of Polymer Science: Part A: Polymer Chemistry, Vol. 31, pg. 619-624 (1993); "High-Solid Alkyds Based on Hyperbranched (Dendritic) Polymers--A New Concept with New Opportunities" by Pettersson et al, presented at the Waterborne, Higher-Solids, and Powder Coatings Symposium, Feb. 9-11, 1994; "Chemistry of Dendritic Molecules Holds Growing Allure for Researchers," Chemical & Engineering News, Feb. 1, 1993; and "Dendrimers Nearing Availability for Commercial Evaluation," Chemical & Engineering News, Aug. 16, 1993.
None of the preceding references teach or suggest the amine-functional polyesters according to the present invention.